“Methicillin-Resistant” Staphylococcus aureus: Reassessment by controlled trial in burns unit

Abstract

A controlled trial of oral flucloxacillin (250 mg six-hourly for four days) was performed in 34 patients treated by the covered method whose burns had yielded a heavy or moderate growth of Staphylococcus aureus resistant to methicillin at 30°C but moderately sensitive at 37°C. Staph aureus was eliminated in nine of the 17 patients treated with fiucloxacillin but in none of the 17 controls; the proportion of patients from whose burns sensitive Staph aureus was eliminated in an earlier trial of cloxacillin was greater than this. Strains of Staph aureus commonly described as methicillin-resistant and showing heterogeneous growth at 37°C of many sensitive and very few resistant bacterial cells should, in the light of these findings, be called moderately sensitive to flucloxacillin. Such “heteroresistant” strains showed consistent moderate sensitivity in replicate diffusion sensitivity tests at 37°C, but very inconsistent results in replicate dilution tests, especially with fiucloxacillin. These studies showed that 18-hour diffusion sensitivity tests indicate the clinical value of treatment with flucloxacillin for staphylococcal infections of moderate severity more correctly at 37°C than at 30°C. © 1977, British Medical Journal Publishing Group. All rights reserved.